Hello all,

I have a Goldberg Sr. Falcon (ARF) that I'm learning to fly on. It's powered by an OS .46 LA. I've joined a club that has a grass field, and the Falcon has difficulty getting off the ground. Basically I have to hold full up elevator while making the takeoff run. (I have dual-rates set up so on high-rate the elevator throw is what the manual recommends for experienced fliers. My instructors and I have only been flying it on the high-rate.) Anyway, once the thing is in the air I ease off on the elevator and climb slowly until it picks up speed and then I climb out. Unfortunately our field has trees near one end of the runway, which makes me really nervous as I have to turn right away to avoid them. Once in the air it flies fine on 3/4 throttle, but one instructor told me that it'd be better if it had more power so I could power myself out of trouble. (But another instructor said that forces me to learn good flying habits.) Also, when shooting approaches I get nervous about the trees when I go around.

I really wish I had bought the OS .46 AX (which is rated at 1.6 bhp) instead of the LA (rated at 1.2 bhp). Unfortunately, I can't really swap engines now unless I do some major surgery to the front end (it has a plywood engine mounting plate (with blind nuts) that's epoxied to hardwood beams).

I am tempted to install flaperons to try to shorten the takeoff run (it already has two aileron servos). Or maybe I'll buy a tachometer so I can safely lean the engine out as much as possible. Or possibly higher-nitro fuel? (I'm using 10% now.)

Any thoughts? Suggestions? Reassurances?

What prop are you using? Bigger wheels also help.

Currently 11x6 (Master Airscrew 11x6 G/F G3). Have also tried Top Flite 11x6 Power Point.

I would experiment more with the props. Most people don't experiment enough in this area, and often have the wrong prop for the engine/airframe combination. Try dropping down to a 11-5 or a 10.5-6 (both are available from APC and a few others) and allow the engine to turn more rpm to get more into it's power band. Slightly more nitro adds very little to the power in sport engines, but increasing the rpm with a prop change will move most engines to a higher power output.

The Sr. Falcon was originally designed to be powered by .35 to .45 sized engines with much heavier radio gear. Add to that, the engines were much less powerful than today's engines. Of course, way back when, they usually had .45's and larger engines up to .60's that had about the same power that you have now.

On heavy grass, tire size does make a difference in ground roll. I've even seen people put skinny vintage style on for this reason (though it looks strange).

OK, I'll give different props a try. That makes sense, as during the takeoff run it's not going very fast so the engine is nowhere near the RPM where it puts out peak power. Bigger/skinner wheels did cross my mind - full scale Cubs, etc. use tundra tires (very big tires) for operating off of rough terrain.

Maybe a combination of better prop and bigger wheels will improve things enough... Also, I suppose I could try JATO (kidding).

Ever see the Blue Angels' C130 do it's JATO takeoff at an airshow? It's a real 'OH WOW!' moment.

The 1.2 hp rating of the engine is at 15,000, so the actual power you are producing at say 11-12 K would be much less. Full size aircraft often have constant speed props, allowing the engine to turn up (and make full rated power for the present conditions). Climb rate of any airplane is proportional to hp (truckers climbing mountains roads are also bound by simular equations).

Good luck, let us know how it turns out.

An 11x6 is way to much prop for a LA 46 try a 10x6 apc I learnt to fly with a Sr Falcon powered by a OS 40 back in the early 70`s and it had good performance using a 10x6 prop but it was hopeless with a 11x6 I currently have a LA 46 in a sport model with a 10x6 apc and has good performance using more than 10%nitro in the LA46 will not add any power to it I would reccomend you try a apc prop

John

No one mentioned this so I will.

I believe that the OS LA 40 is way undersized for this plane. The Sr. Falcon is a large aircraft, and getting that size plane off the ground in grass is a challenge. I would opt for at least an OS 46 AX or the new OS 55 AX engine and prop it accordingly. Especially if you are flying in a limited area as you say you are.

I know that the OS 40 LA may be the recommended power for that plane, but you obviously have seen that it lacks somewhat in the power band using standard props, and getting it up to 16,000 RPM to get into it's power band is not practical... especially if you want to keep that engine running for longer than a few months.

you can also remove the baffle in the muffler, that should get you another 1,000 rpm's

sr falson used to be a .60 size airplane ,how much does your plane weigh,what size wheels are you using?when sitting at rest is the chord line of the wing level with the ground,pointed down torwards the ground or pointed up.I have a feeling you are using wheels that are too small and the nose gear strut is too short.on a grass field minimum wheel size should be 2 3/4 longer grass means larger wheels.also the plane will take off easier if the nose gear is lengthed a bit so that the plane sits slightly nose up.I flew a 5 1/2 pound falcon 56 on an os 35 r/c for 2 years back in 1970 off a grass field and these things helped.

I don't know how much it weighs. I did have to add about 9 oz of nose weight to get the CG in the middle of the recommended range (despite putting the battery under the tank) - I'm guessing this is because it was originally designed for a .60. According to Tower Hobbies the wheels are 2.75", although I haven't confirmed this. It does sit a little nose-down, despite the nose gear being as far out as I can put it.

Oh, what size tires do people recommend? Looks like with Dubro tires I can go a number of sizes bigger and still have the same axle size.

I'm leaning towards 3.25".

you can try 3 1/4 and see what happens but of the nose is sitting down at rest you will still have the same problem of applying enough up elevator to get the nose to rotate to a take off position.dubru used to make a long nose gear strut that allowwed you to lengthen the nose gear in situations like this.see if you can fit this in place of what you have.
http://www2.towerhobbies.com/cgi-bin...&I=LXD844&P=SM

I am with aerowoof, if your nose is down that is the reason you are having trouble getting off the ground.
With that attitude your plane is trying to fly into the ground.
Fixes?
Longer nose gear
Shorter main gear
Larger nose wheel
Smaller main wheels
Whatever it takes get that nose up to where the wing is at least level with the ground.

Perhaps the larger engine is in order. I don't think removing a muffler will help much.

I flew my Senior Falcon a couple of times today.

It has a 46 ax on it. The my wheels are 3.5 inches. The nose gear was replaced with a better sig unit. Replacing the original nose gear will help out tremendously on controlling the plane on the ground. There is too much play in the original nose gear.
My 46 ax will pull the Senior around the sky at 1/2 throttles at a pretty good clip.

You may be trying to get the plane in the air before it has picked up sufficient air speed. Force the plane to stay on the ground. Your trainer can show you how. Once you get sufficient speed then and only then apply some up elevator.

You may have to give it a little push to get it rolling. Once it is rolling keep it straight into the wind.

The Senior is a fun plane.

Try the bigger wheels, replace the nose gear, and get sufficient ground speed before you take off. I think your engine will be okay.

Take offs and landings are the toughest parts of learning to fly. Do not get discouraged.

bob

You may not realize this, but holding full up will actually slow down the takeoff run rather significantly. In addition, it creates a situation where the plane will takeoff before it has adequate flying speed, exposing it to an unexpected snap roll.

Since the plane sits with a nose high attitude, try leaving the elevator at neutral until the plane has developed enough speed to takeoff. Once it's at speed, you should be able to pop it off the runway with just a little up elevator.

This is the smallest recommended prop for this engine, so it should be in about the right range. If you want to allow the engine to spin a little more, you could try an 11x5. I don't think I would drop down into the 10 inch range, it would likely develop less thrust and therefore less acceleration on takeoff.

Slightly larger wheels could help it get through the grass better. Don't worry about it being nose down, that helps it stay on the ground when it lands. If you want to try raising the nose, just put a slightly larger wheel on the front. If you do raise the nose, do not make it any higher than level.

If the baffle can be removed, and then put back in, this would be worth a quick test. Remember that removing the baffle will reduce back pressure, which will reduce fuel pressure, which will lean the engine out a bit. To make sure that you're truly testing the effect of removing the baffle, instead of just leaning the engine a bit, set it a bit richer. Borrow a tachometer from someone so you can measure before and after.

Hi!
A MA 11x6 is not that good prop!
A much better prop is a 12x4 APC or 11x6 APC.
But ...have you checked your Cof G ?It sounds to me that your airplane is too nose heavy if you have to apply full up elevator to just get of the ground...

Ditto to what acarter said. Take out the baffle. I have done this on numerous LAs with tremendous increases in power. The last time we did it to a .25 LA, we tached it before and after and got 1600 rpm. It is really easy to do. there is a long bolt that runs through the muffler front to back. Unscrew it and separate the two parts of the muffler. The baffle is a cone shaped part inside. Take it out and reassemble. You will have to adjust the needle some because you do have less back pressure. It will be a little louder, but not bad.

What everyone else has said is true. 11X6 is too much prop. Go to a 10X6.

On the takeoff run it seems to reach a speed where it just won't go any faster. It seems like lifting the nose wheel off the ground during the takeoff run allows it to accelerate a little more. Once it's in the air it's flying very slow but I ease off the elevator and it picks up speed.

Right now it's marginal but doable. I figure even a small increase in power and/or decrease in rolling resistance should produce a significant improvement.

Anyway, I'm gonna try the lager wheels and a few different props.

Try the baffle removal. You will get a significant increase in power. If you don't like it, it takes 30 seconds to put back in.

Yeah, if it's not against club rules I'll give that a try too.

Not sure what kind of noise restrictions your club has, but I wouldn't think it would be a problem. It doesn't make it that much louder and it is still much quieter than a gasoline engine.

Good luck.

I had a Senior Falcon that took off from grass easily and did outside loops on an OS 40 FP. It weighed 5 1/4 lbs and balanced at the rear end of the CG range, which worked just fine. Absolutely delightful airplane (see my gallery).

Try removing some of that lead and getting the CG back. I bet the modern plans show a very conservative CG. I just checked my log book and I had it at 4 1/2 inches from the LE. If your CG is ahead of that, then moving it back will not only decrease weight, but make the plane aerodynamically more efficient.

Also, 6 inches of prop pitch is too much. If your engine will swing an 11x6 prop, then it will also swing a 12x4, which will give much more thrust on a big, slow flying airplane.

I assume you're using light weight foam wheels, right? Do everything you can do to keep down weight.

Jim

I went back and saw that you said you would experiment with props. Let us know the results. I don't mean to try only the 12x4 - an 11x5 is certainly worth trying too. It would help if you could weigh the plane too.